Engines, including diesel engines, gasoline engines, natural gas engines, and other engines known in the art, may exhaust a complex mixture of air pollutants. The air pollutants may be composed of gaseous and solid material, which may include particulate matter. Particulate matter may include unburned carbon particles, which are also called soot.
Due to increased attention on the environment, exhaust emission standards have become more stringent. The amount of particulates emitted from an engine may be regulated depending on the type of engine, size of engine, and/or class of engine. One method that has been implemented by engine manufacturers to ensure compliance with exhaust emission standards has been to periodically sample the emissions of engines within test cells.
One such method is described in U.S. Pat. No. 5,546,788 (“the '788 patent”) issued to Dickow on Aug. 20, 1996. The '788 patent introduces a method and apparatus wherein a sample of engine exhaust gases is diluted and aspirated through a measuring device in which the quantity of solid particles (particulate matter) is measured. The actual quantity of the exhaust gases in the total quantity of aspirated gases flowing through the measuring device is determined, in a by-pass phase when the exhaust gases are cut-off, by measuring the amount of substitute outside air which replaces the exhaust gases flowing through the measuring device. The concentration of the particles in the exhaust gases is determined from the ratio of the measured quantity of solid particles and the mass flow of the air measured in the mass flow meter.
The method and apparatus of the '788 patent may not perform a self-check step to determine the accuracy of the apparatus. Because the accuracy of measuring devices may drift over time, the ability to perform a self-check to determine accuracy and/or calibrate the apparatus prior to actual testing may be important in obtaining accurate test results.
The particulate sampling system of the present disclosure is directed towards overcoming one or more of the problems set forth above.